(1) Field of the Invention
The present invention relates to an electroluminescent lamp and a process for fabricating the same, and more particularly to an ultra-thin electroluminescent lamp without using outer coat films and a method for fabricating such lamp.
(2) Description of the Related Art
A conventional electroluminescent lamp of the kind to which the present invention relates is first explained to assist the understanding of the present invention. As shown in FIG. 1, the conventional electroluminescent lamp 30 is configured such that an electroluminescent element 27 in the form of a laminator and generally in a rectangular shape in a plane view, as described later, is sealed with outer coat films 28 and 29 formed of fluororesin or the like having moistureproof property.
The electroluminescent element 27 is formed by laminating a rear electrode 21, a reflective insulation layer 22, a luminous layer 23, and a transparent electrode 24 in this order from the under side. The numerals 25 and 26 in FIG. 1 denote hygroscopic layers which are constituted by hygroscopic films of such as polyamides and are respectively disposed on the top and the bottom of the electroluminescent element 27. Generally, an electroluminescent lamp is formed in the form of a thin flat-panel luminescent body, and the thickness thereof is approximately 1 mm. However, when such luminescent body is used for a backlight for a liquid crystal display for use in pocket bells, pagers and the like, it is required for the luminescent body to have a thickness of approximately 0.3 mm. What has been done conventionally to meet such requirement is to make the hygroscopic films 25, 26 and outer coat films 28, 29 as thin as possible within the limit of the moisture-proof capability.
However, for reducing the thicknesses of the hygroscopic films and the outer coat films in the ways as described above, there is a limit in the reduction because the life is affected under high moisture environment. Thus, the limit to the thickness of the electroluminescent lamp has been 0.8 mm for maintaining the reliability under high moisture. For solving this problem, many attempts have been made to reduce the thicknesses of respective layers or to omit package films. For example, by changing the transparent electrode or the rear electrode to that of a printed-type using electrically conductive paste, it is possible to make such reduction by the thicknesses corresponding to the materials used for a transparent film and the metal foil used for the rear electrode. However, the thickness that can be reduced thereby will be only in the order of 0.1 mm. In addition, as described in Japanese Utility Model Application Kokai Publication No. Sho 63-112795 and Japanese Patent Application Kokai Publication No. Hei 2-276193, when the printed-type is used, the luminous layer and the reflective insulation layer tend to have pin holes resulting in deterioration of insulation characteristics, so that a process for flattening such layers is additionally required. In another example, as disclosed in Japanese Patent Application Kokai Publication Nos. Hei 2-38482 and Hei 4-230996, the outer coat films are omitted by using phosphor microcapsuled with an oxide compound having moistureproof property for the luminous layer. Although the use of such phosphor enables to omit the outer coat films, the high dielectric resin used for a binder has high hygroscopicity under high humid conditions and this causes various problems such as water penetration, short-circuitting, excess current flow and element breakdown.